1. Field of the Invention
The present invention relates to flexible electrical conductors, particularly, superconducting wire bundles within a flexible cryostat.
2. Description of the Background Art
Lightweight conductors that transmit large amounts of electric current without significant loss have numerous applications. For example, in electro-refining applications such as aluminum production processes, high amounts of current are required. Other applications requiring light-weight, high-current conductors are naval ships. Naval ships, typically formed of ferromagnetic materials and thus having a substantive magnetic field, are outfitted with complex systems of electromagnetic windings referred to as degaussing cables which serve to reduce the magnetic field of the ship. This permits the naval ships to evade magnetic sensitive ordinances or devices such as mines that are triggered by the ship's large magnetic field.
To accommodate the high-current requirements in the exemplary applications described above, large diameter wires, typically made of copper or aluminum, are generally utilized. However, this leads to undesirably heavy, bulky, and inflexible cables. Recently, it has been proposed to replace the large diameter conventional wire cables with conductors formed of high-temperature superconducting (HTS) materials. As used herein, a high temperature superconductor (HTS) material refers to a material that can maintain superconducting behavior at temperatures of 20 K and higher (i.e., critical temperature, Tc≧20 K). HTS cables are disclosed in co-pending U.S. patent application Ser. No. 11/880,567, the contents of which are incorporated by reference herein. Accordingly, the HTS cables afford greater flexibility, reduced weight, and high current carrying capacity, thereby having significant advantages over the conventional wire cables.
Such HTS cables generally include a flexible cryostat, in which is disposed a plurality of superconducting conductors. For example, the conductors may be provided as flat wires (tapes), and a plurality of flat wires are arranged in layers to form a stack of HTS flat wires. Two or more stacks of HTS flat wires may be arranged together to form a stack superstructure. The stack superstructure is maintained in the desired configuration by providing the conductors with an outer insulative wrap, whereby an HTS wire bundle (cable) is formed. One or more HTS wire bundles are disposed within the cryostat, which is configured to maintain the individual HTS wires at a temperature which permits the HTS wires to exhibit the property of superconductivity.
However, in order to facilitate assembly of the HTS wire bundle within the cryostat, and to provide a coolant flow path along the length of the HTS wire bundle, the inner diameter of the cryostat is generally somewhat larger than that of the outer dimension of the HTS wire bundle disposed therein. This can be problematic since, in use, the HTS wire bundle is subject to vibration which causes degradation in bundle insulation over time. In some cases, such degradation leads to undesirable conductor-to-conductor or conductor-to-cryostat short circuits. Moreover, localized insulation wear also occurs at intervals along the length of the HTS cable at locations corresponding to that of cable retaining members.